Giant rats to sniff out tuberculosis, Mozambique prisons

Tuberculosis is the leading cause of death, after HIV, from an infectious disease. Around the world, there are about 9 million new cases a year and around 2 million deaths, according to the World Health Organization.

Scientists in East Africa plan to exploit trained rats’ highly developed sense of smell to carry out mass screening for tuberculosis among inmates of crowded prisons in Tanzania and Mozambique.

African Giant Pouched Rats trained by the Belgian non governmental organisation APOPO are widely known for their work sniffing out landmines, and are now developing a reputation in East Africa for their skill and speed at detecting TB too.

Tuberculosis is the leading cause of death, after HIV, from an infectious disease. Around the world, there are about 9 million new cases a year and around 2 million deaths, according to the World Health Organization.

In Tanzania, people in communities where TB is most common, including prisons, often fail to show up for screening because of lack of money or awareness, creating a huge burden for health authorities trying to tackle the disease, health officials said.

Because existing systems lack the accuracy, speed and cost-efficiency required to scale up screening of the highly contagious disease, many TB cases go undiagnosed, they said.

APOPO, with funding from the United States Agency for International Development (USAID,) plans to recruit and train more rats to carry out prison screening that it expects to be faster and more reliable than existing methods.

"We then aim to expand the programme to all prisons, shantytowns, factories and other settings in Tanzania, Mozambique and other high TB-burden countries, as well as in high-risk groups such as those individuals living with HIV/AIDS. This will improve and save lives all over the globe at a low cost,” Richter said.

Though data from African jails is hard to come by, studies from Tanzania, Malawi and Ivory Coast show that TB rates are 10 times higher in prisons than in the general population, according to the US Centre for Infectious Diseases Control.

TRAINING STARTS AT FOUR WEEKS OLD

APOPO says the rats undergo a rigorous training process that begins when they are four weeks old. As soon as the rats open their eyes, they are introduced to various stimuli and learn how to socialize and interact with people.

The rats learn to recognise the presence of TB in samples of sputum, mucus that is coughed up from the patient’s lower airways, and rewarded when they succeed.

The testing process starts when a rat is presented with a row of 10 sputum samples, and when it detects TB the rat hovers over the sample for 3 seconds, Richter said.

The rats' accuracy at detecting TB is almost 100 percent, but they cannot distinguish between normal and drug-resistant strains, APOPO scientists say.

The APOPO system is fast, cheap and has the potential to greatly lower screening costs in poor countries, Richter said.

While a laboratory technician may take four days to detect tuberculosis, a trained rat can screen 100 samples in 20 minutes, and a rat screening can cost as little as 20 US cents when APOPO operations are running near capacity, he said.

APOPO’s current programmes have screened more than 340,000 TB samples, halting over 36,000 further infections, and increased detection rates by over 40 percent in several partnered clinics, officials said.

Khadija Abraham, an expert at Tanzania’s National Leprosy and Tuberculosis Programme, said trained rats had a great ability to detect a wide range of strong-smelling molecules that could help tracking down undiagnosed TB cases, especially in rural areas.

"Training an animal with a strong and reliable sense of smell to help detect disease in a vast country like Tanzania could potentially offer a valuable solution to help detecting the disease," she told the Thomson Reuters Foundation.

Training pouched rats requires little human skill since they only have to be exposed to the smell they need to recognize, Abraham said.

“Experiments show that these rats can detect a sample with TB parasites in a second and evidence has shown that they are able to sniff out even those with very minimal parasites,”she said.

TB cases are normally detected by sputum smear microscopy, a slow and costly process that has not changed for years and is not very accurate. The WHO insists that one lab technician should not test more than 20 patients a day, and says the chances of misdiagnosis are high if this exceeded.